MATLAB SYSTEM IDENTIFICATION TOOLBOX 7 Guide de l'utilisateur télécharger pdf (Page 177)

100

101

Modeling Multiple-Output Systems

After validating the single-output models, use vertical concatenation to

combine these partial models into a single multiple-output m odel. For more

information about concate na tion, see “Conc aten a tin g iddat a Objec ts” on page

1-65 or “Concatenating idfrd Objects” on page 1-71.

You can try reﬁning the concatenated multiple-output model u sing the

origina l (mu lti pl e- output) data set.

Improving Multiple-Output Estimation Results by

Weighing Outputs During Estimation

When estimating linear and nonlinear black-box models f or multiple-output

systems, you can control the relative importance of output channels during

the estima t ion process. The ability to control how much each output is

weighed during estimation is useful when some of the measured outputs

have poor accuracy or should be treated as less important during estimation.

For exam p le , if you ha ve already modeled one output w ell, you might want

to focus the estimation on modeling the remaining outputs. Similarly, you

mightwanttoreﬁne a model for a subset of outputs.

You can s pe c if y outpu t weights directly in the esti mation command using

the

Criterion and W eigh ting ﬁelds of the Algorithm property. You must

set the

Criterion ﬁeld to Trace, and set the Weighti ng ﬁeld to the matrix

that contains the output weights. The

Trace criterion minimizes the weighted

sum of the prediction errors using the weights speci ﬁed by

Weighting.

The following code snippet shows how to specify the

Criterion and Weigh ting

Algorithm

ﬁelds as part of the pem command:

model=pem(z,2,'criterion','trace','we ighting',diag(Q,1))

where Q is a vector of positive values and the higher values for outputs to be

emphasized more during estimation.

You set

Weighting to a positive semi-deﬁnite symmetric matrix of size equal

to number of outputs. By default,

Weighting is an identity matrix, which

means that all outputs are weighed equally during estimation.

For more information about these Algorithm ﬁeldsforlinearestimation,see

the

Algorithm Prope rtie s reference page. For more information about

2-23

1 2 ... 172 173 174 175 176 177 178 179 180 181 182 ... 530 531

Commentaires sur ces manuels

Pas de commentaire

MATLAB SYSTEM IDENTIFICATION TOOLBOX 7 Guide de l'utilisateur Page 177

Commentaires sur ces manuels

Produits connexes et manuels pour Logiciel MATLAB SYSTEM IDENTIFICATION TOOLBOX 7